Remove invalid log "Failed to executing diff command: exit status 1"

[aledbf]

What this PR does / why we need it:

From http://man7.org/linux/man-pages/man1/diff.1.html Exit status is 0 if inputs are the same, 1 if different, 2 if trouble.

This is interpreted as "error" but this is true only when the exit code is 2

[codecov-io]

Codecov Report

Merging #4416 into master will decrease coverage by 0.03%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #4416      +/-   ##
==========================================
- Coverage   58.64%   58.61%   -0.04%     
==========================================
  Files          88       88              
  Lines        6572     6572              
==========================================
- Hits         3854     3852       -2     
- Misses       2288     2291       +3     
+ Partials      430      429       -1

Impacted Files	Coverage Δ
internal/ingress/controller/nginx.go	29.07% <0%> (-0.14%)	⬇️
internal/watch/file_watcher.go	80.76% <0%> (-3.85%)	⬇️
internal/ingress/metric/collectors/process.go	88.29% <0%> (-2.13%)	⬇️
internal/ingress/controller/store/store.go	60.22% <0%> (+0.63%)	⬆️

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[aledbf]

/test pull-ingress-nginx-e2e-1-15

[ElvinEfendi]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, ElvinEfendi

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[aledbf]

/test pull-ingress-nginx-e2e-1-15

[aledbf]

/test pull-ingress-nginx-test

[aledbf]

/test pull-ingress-nginx-test